I'll Be Your Detonator
by celestialghostie
Summary: Jim Moriarty never imagined that his life would be turned upside down by anyone other than Sherlock, but when he runs into Sebastian Moran, a newly turned vampire with no idea of his own capabilities, he realises that he has discovered the perfect weapon.
1. Prologue

**Prologue**

As twilight faded into an encompassing darkness, James Moriarty stepped out onto the streets of London. The streets that were bustling, filled with nothing but boring people only a few hours ago were now much more subdued. However, nighttime was when the more interesting people came out to play, and Jim loved to watch them, listening to their little plans and mentally correcting their frankly laughable mistakes. Most of them were stupid, but at least London's so called 'criminals' provided him with a certain degree of entertainment.

Neon lights from clubs and bars flooded the streets; the fluorescent signs reflecting in the rain-kissed pavements. Jim opened his umbrella, glad of the shelter it provided him from both the cold showers and the eyes of the passersby. Nobody interesting ever gathered in the clubs, and he did not fancy initiating a conversation with some petty crook. He briskly walked past the colourful venues, turning to the left and heading down a much quieter avenue. This was more like it.

Under the haze of black cloud that danced over the moon, he felt utterly at peace. Nighttime was when people stopped pretending, and James was no exception. He loathed having to pretend to be an ordinary person who had an ordinary person job and lived an ordinary person life; it was enough to make a man mad. The darkness of the city at night was his escape.

As he rounded another corner, the streets became narrower. The harshness of the sickeningly bright signs was suddenly replaced with the dull glow of streetlights. The only sounds to be heard were the distant thrum of traffic and the muted conversation coming from the apartments he passed. Jim was accustomed to seeing someone attempting to break into one of the ground floor apartments, but it seemed as though those pathetic people had some other plans in their dull, little lives. He rolled his eyes. London would have to answer for not entertaining him, but first he had to make the tedious trek back to his complex. Turning on his heel, he grumbled something about the state of the underworld these days and was about to begin plotting against the lackluster city when suddenly from the gloom there came a scream.

A smile crept onto Jim's face. Oh, how he'd hoped London wouldn't disappoint him for the third night in a row. He followed the delightful sound through the winding labyrinth of cobblestone lanes and back alleys, resisting the urge to hum merrily as he went. The best type of idiot to watch was a killer. Most of them didn't have a clue what they were doing, and it was hysterical watching them trying to play out their crime in the way that they'd dreamed about it. They never succeeded. Poor things.

Another scream.

Jim came to a stop at the entrance to another alleyway, and he watched the scene in front of him unfold in a silent fascination. In the dim light that oozed through the narrow gaps in the brick walls, there was a man. He stood hunched with his back to Jim, the shadow of the night hiding his victim from sight. Shrugging, Jim approached the man as quietly as he could. His heart raced as he stood a mere metre behind him, the telltale smell of iron filling his nostrils, and yet he still couldn't see the body. The man held their victim close, almost cradling the body in their arms. If there was anything he hated more than clueless killers, it was dull ones. Becoming decidedly bored, Jim let out a huff of air and moved to walk past the man.

"Next time, at least let a guy watch, jeez..." Jim drawled.

The man snapped his attention up to the consulting criminal in a blur of animalistic panic, and he felt a rush of excitement course through his veins. The man's eyes were wide, like a deer caught in headlights, and he clung to the lifeless body even tighter. Perhaps he would get some entertainment after all. Usually he got told to 'fuck off' if he made a snarky remark to a killer after a hunt, but this one simply stared at him in an almost innocent bewilderment that captivated him. As he crouched down beside the man, Jim saw something that made the innocence fade ever so slightly. The man's face was covered in blood. The crimson liquid was smeared around his mouth, coating the tongue that darted out to wet his lips so that he could try to speak, but he couldn't seem to find the words. It was almost as though he was a child searching for an excuse for misbehaving. In that one harmless motion, Jim saw something that spoke to him more than any words ever could. A flash of white belonging to two sharp, elongated canines.

Gesturing nonchalantly at the body, Jim peeled the woman away from the man's clutch, examining her thoroughly as the killer watched on in a shock induced trance. Her corpse was waxy, the only colour the deep red that spilled from her throat. Jim regarded the sight in front of him and quietly contemplated what he should do, for hidden beneath tendrils of matted hair, the woman's neck was decorated with two perfect puncture wounds.

"You really must let me watch next time, you know." Jim straightened up, brushing off his suit as he did so. He held a hand out to the man who was still gawping at him, his lips curling into an amused smirk. "James Moriarty. You can't wander around London on your own looking like that, you'll get locked up or attacked. No one will even dare look at you if you walk with me. Now, where are your manners, hm? I told you my name."

The stranger hesitated, but hastily gripped onto his hand. As he helped the man to his feet, Jim leaned in closer to study his face. He was a fair bit taller than Jim, yet despite his obvious advantages he still looked scared. Lost, even.

"It's Moran." The man muttered, his voice barely audible as he struggled to keep his canines hidden. "Sebastian Moran."

The smile on Jim's face stretched wider.

"Good. Once we've worked on your table manners, I have a proposition for you, Sebastian Moran."


	2. Chapter 1

**A/N:** **Just wanted to say a quick thank you to everyone who read, especially those who told me to continue! I hope you enjoy the next part, and I will try my best to upload every other day!**

 **Chapter One**

"Once again, Sebastian, it's perfect." Tracing his fingers over the battered dummy target, Jim lightly prodded at each of the bullet holes. "I really don't think there's any way for you to improve in these conditions." He paused, turning on his heel to face his new pet with an almost childlike smile. "How do you feel about live target practice, Sebby?"

Sebastian ran a hand through his hair, exhaling shakily through his mouth. "I'm not so sure, boss... If I hit them then they're going to bleed, and I-... I can't afford to let my concentration falter. Not if you want me to be going outside and mixing with other humans to carry out jobs for you." Flashes of the night his boss saved him came flooding into his vision, and Sebastian grimaced as a deep feeling of shame manifested in the pit of his stomach. He had been a mess. An uncontrollable, starving, abhorrent mess. And he never wanted to feel that way again. At least with using a rifle he had control over the death, and was consciously choosing to take someone's life rather than being overruled by thirst. Shooting was so much less personal, and Sebastian was more than used to handling firearms from his days as colonel. He dug his nails into the palm of his hand; he couldn't afford to think back to then. He'd blocked it out until now, and frankly he didn't want to remember how the night he got attacked by that bloodsucking parasite went down.

"You'll have to get used to the smell of fresh blood eventually, Sebby." Jim mused, his eyes dancing around the training centre. His gaze stopped at one of the few guards he'd allowed into the facility, and he jerked his head to the side, watching intensely as the guard came to stand in front of him. "People have silly little accidents all the time. A papercut, a fall, a graze... Isn't that right, Fletcher?"

The guard- Fletcher- nodded slowly. Jim could see the fear shimmering in his eyes and oh, it was beautiful. He sidled up to his guard with a sweet smile, resting a hand on his shoulder in a gesture that in any other situation would have been seen as comforting, but the devilish taunt behind Jim's smile made the simple touch burn with a cruel mocking of what was to come.

"You have to be prepared for anything, Sebastian. Someone will be bleeding to some degree wherever you go. Think of this as a lesson in self control."

Fletcher flinched as Jim patted him on the cheek, the patronising contact making bile rise in his throat. Feeling a slight scratch, the guard looked down to see a miniscule puncture mark where Jim had pushed a drawing pin through the skin on the back of his hand. Blood rushed to the surface, and Fletcher hastily brought his hand to his mouth, sucking at the scratch before Sebastian could notice.

But it was too late.

That single note of blood sang to Sebastian, and who was he to ignore its call?

Jim turned away, idly looking through his phone messages as chaos exploded behind him in a fit of screams and sobs. "We're going to have to work on your self control, 'Bastian." He chided, not looking up from his phone screen. "Otherwise I'm going to have to keep you on a silver leash."

The sniper had definitely come a long way from the hollow shell of a person he was a few months back, but Moriarty knew that he would have to keep working at him for a few months more before Sebastian was fit for showing off. Yes, he was showing incredible agility, strength, and accuracy in his training, but the poor man needed rebuilding. He needed to be guided and molded so that he wasn't afraid of his newfound abilities. He needed to be shaped into the perfect weapon that Jim knew he could be.

His perfect weapon.

* * *

"Sebby, are you coming with me to visit him or not?" Jim whined, hands buried deep in his pockets. He'd been stood outside his sniper's room for ten minutes now, trying to coax him out. "C'mon, you know I'm not going to let you hurt him..."

Four long months had passed since the 'incident' with Fletcher, and Sebastian was so much more accustomed to his new life now. It was almost as though he'd been a vampire all his life. Well, apart from the odd slip up.

"Boss, you know that you can't hold me back if I snap... How do you know that I'm going to be able to keep myself under control?"

"I know, because for the past seven months you have proven to me time and time again that you're controllable if you've fed the week before." Jim toyed with the small black box in his pocket. "Your last full feed was ten days ago, but I have something here to make sure that you're on top form."

Interest piqued, Sebastian slowly opened the door to his room, sighing heavily. "I don't want to hurt him, not with the way you talk about him."

"I'm not going to let you hurt him, Sebby. Besides, he's got a pet that I don't care much for. You could always attack him." Jim flipped the small, velvet box open, revealing the syringe that lay inside. He slowly removed it from its case, turning it over in his hands. His voice suddenly took on a warning tone. "Don't expect this to become a frequent affair, 'Bastian. I just don't want you hurting my darling detective." Rather nonchalantly Jim began to draw blood from his arm, watching Sebastian closely as the syringe filled.

He was completely entranced.

"You really shouldn't do this, boss." Sebastian felt a lump rising in his throat, and grit his teeth against the feeling. He was right; Jim _really_ shouldn't have done that. An overwhelming desire to just rip the needle from his arm and tear his boss' flesh apart crashed into him, and it took every ounce of his willpower to hold himself back.

"Too bad." Jim disposed of the needle, handing Sebastian the small vial of his blood. "Drink up."

The moment a drop of blood kissed his tongue, Sebastian was dead to the world. Never before in either of his lives had he tasted something so exquisitely divine. His body instantly warmed, and a healthy glow spread across his ashen skin as his body absorbed the nutrients from the small mouthful of blood. It took all of Sebastian's restraint to not ask his boss for some more; he knew he was incredibly honoured to have been offered the vial and he didn't want to ruin that, so instead he focused on the sweet, tangy taste that coated his mouth.

"Thank you, boss."

"You're welcome." Jim studied Sebastian's face and struggled to hide his amusement at the expression he was making. He looked like a child who had found a secret stash of candy. Clearing his throat to disguise a chuckle, he linked arms with his sniper, a newfound spring in his step as he lead Sebastian out of the training facility for the first time in seven months. "You're going to love Sherlock, Sebby. But I want you to try to get close to his pet. Johnny boy is the key to unlocking our first game together~."

 **A/N: So, what did you think? I'd love it if you left a review to let me know; they encourage me to keep writing!**


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